1. Field of the Invention
The present invention relates to an image pickup apparatus and an auto-focus detection method.
2. Description of the Related Art
For auto-focus (AF) control in an image pickup apparatus such as a video camera, a TV-AF system has been mainly used that generates an AF evaluation value signal representing the sharpness, contrast state, etc. of an image signal generated by an image pickup device and adjusts focus lens position so as to attain the maximum of the AF evaluation value signal.
When photographing a person with an image pickup apparatus that performs AF control, focusing is sometimes made not on the person (main object) but on the background depending on a state of contrast between the person and background. In that case, the focusing cannot be achieved as desired by the photographer, giving a discomfort to the photographer.
To obviate this, an image pickup apparatus has been proposed that recognizes a face in a picked-up image, sets a focus detection area including the recognized face, and performs focus detection based on the focus detection area (see, for example, Japanese Laid-open Patent Publication No. 2006-227080). Another image pickup apparatus has been proposed that detects a human face (especially eyes) in a picked-up image and performs focus detection based on the detected eyes (see, for example, Japanese Laid-open Patent Publication No. 2001-215403).
The resolution of picked-up image tends to be affected by an imaging state. With the aforementioned image pickup apparatuses, if hand-shake is caused at high zoom magnification photographing, the resolution of picked-up image is lowered to make it difficult to detect a face to be photographed.
If a face is not detected, focusing cannot be performed by the image pickup apparatuses, posing a problem that it becomes impossible to make focusing on the main object (face) even though the main object is present on the imaging screen.
In a case for example that face detection and non-detection are irregularly repeated depending on imaging state, focusing is made on a face when the face is detected but on the background when no face is detected, posing a problem that stable focusing on the object cannot be achieved.